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<br />a <br />• ~ testing, particles larger than 318 of an inch were substituted with material between the <br />No. 4 and 3/8-inch sieves. The removal of material smaller than the No. 100 sieve will <br />shift the gradation curve downward as shown on Fig. 1. The estimated gradation of <br />the Lorencito coal waste shown on Fig. 1 accounts for both of these influences. <br />Results of a standard Proctor moisture-density test (ASTM D 698) are shown <br />on Fig. 2. The double "hump" illustrates the difficulty in applying Proctor methods <br />to a granular material with little fines. The lack of fines should result in a relatively <br />flat Proctor curve, however fines are created during testing. The maximum dry <br />density is relatively low compared to previous testing at the RDA but could be <br />attributed to the lower amount of fines. The optimum moisture content is relatively <br />high compared to previous tests. The moisture content at the "lower hump" at 12 <br />percent is closer to the optimum moisture contents found in previous testing which <br />were on the order of 9 to 14 percent. The processing, handling, and placement and <br />compaction of the coal waste in the RDA will generate some fines within the material. <br />We believe compaction should be judged based upon tests performed on material <br />obtained from test locations in the RDA. <br />The results of direct shear testing of the coal waste sample are shown on Fig. <br />3. Peak strength cohesion of 200 psf and friction angle of 36 degrees were <br />measured. The material was flooded and tested at a density of approximately 90 <br />• percent of the maximum standard Proctor dry density. <br />We performed specific gravity testing of 3 large particles from the coal waste <br />sample. The particles were selected visually to represent "typical" coal, shale and <br />sandstone fragments. The bulk specific gravity measured was 1.6 for coal, 2.3 for <br />shale, and 2.4 for sandstone. <br />Analysis <br />• <br />The previous investigation included stability analysis of the existing and <br />proposed RDA configuration. Figure 4 shows the results of the current direct shear <br />testing compared to 9 previous direct shear tests of coal waste from the Golden <br />Eagle Mine. The strength determined for the proposed Lorencito Coal Mine waste <br />(~ = 36 degrees, c = 200 psf) is slightly higher than the normal value used in the <br />previous analysis (~ = 32 degrees, c = 200 psf). Based upon the results of the <br />previous analysis and considering the strength value determined in this evaluation, <br />we believe a static factor of safety greater than 1.5 exists for the proposed RDA. <br />Adequate factors of safety are also implied for the water and earthquake conditions <br />evaluated in our previous investigation. <br />LORENCITO COAL MINE <br />COAL WASTE <br />CTL? 25,852 2 <br />